1. Field of the Invention
This invention pertains to a liquid sight monitor for monitoring the presence of a liquid system and more particularly to such a monitor that can be utilized in adverse climate conditions.
2. Description of the Prior Art
Liquid sight monitors can generally be categorized as either liquid level gauges or as sight flow indicators. Liquid level gauges typically employ a transparent tube and are connected externally to a tank or other vessel, both stationary and transportable, usually metal, but in all events to a vessel having opaque side walls, such gauge providing means to meter or measure the level of the liquid in the tank. A tank depth of 25 feet or less can be passively monitored utilizing a vertical tubular element of transparent material connected by bypass connections to valve connections extending from the tank. Such a tube provides ready observance of the level of the liquid within the tank without having to employ a dip stick, internal reading to a line or the like. Deeper tanks can be similarly monitored using a series of tubes.
Sight flow indicators are generally used for the purpose of revealing to the observer if liquid is present and flowing in an opaque pipeline or conduit. Coincidentally, if the line is flowing at less than full capacity, the actual flow rate can also be observed. A sight flow indicator, like a liquid level gauge, is usually connected into the system which it monitors by way of a bypass connection.
So as to provide protection for the glass or plastic tubing used as the transparent element in which the monitored liquid is located and through which the liquid is observed, it is common to use tubing of short lengths, and therefore not as susceptible to breakage as longer tubing lengths, and/or to shield such tubes with a metallic shield having only a small slot therein to observe the liquid in the tube.
Under favorable environmental or climatical conditions, prior art monitors are generally acceptable. However, under unfavorable temperature and humidity conditions, there are problems. Frost conditions on the outside of a tank can cover up the monitor element and ice can even form from the frost. If the inside liquid is warm and the outside temperature is cold, the plastic or glass can crack, break or discolor in use. Similar unfavorable events can occur where the outside conditions are extremely hot and/or humid. The monitor or sight element can sweat and fog up and if the temperatures are extreme, the element could crack and break through expansion.
To correct for the cold environmental effects that are adverse to normal operations, a steam line has been employed in the prior art adjoining the sight element to keep the glass clear of frost. This technique even works for hot environmental operating conditions to minimize fog condensations.
It can be recognized, however, that a steam line can be expensive and could itself have maintenance problems attendant to leaks and the like. Moreover, the steam line itself may deteriorate or crack the sight element because of the high temeprature environment it itself induces.
Double glass tube structures have been employed in the prior art, but such tubes have not employed insert ends, such as used herein, which seal against both the inside and outside tube by resilient means, thereby providing cushioning to both tubes, and which further provide the capacity to fit connections over a range of sizes and to expand and contract without adverse effect on the tubes. Prior art double tubes, on the other hand, have been contiguous, designed for double flow passage or end connected to each other so as not to achieve the benefits of the inserts herein provided.
Therefore, it is a feature of the present invention to provide an improved, completely passive, liquid sight monitor for presenting a clear sight element even in adverse environmental conditions.
It is another feature of the present invention to provide an improved liquid sight monitor by providing a double tube sight element, the annulus between the tubes being environmentally spaced apart and sealed, while allowing accommodation to connectors over a small range of lengths and to permit expansion/contraction of the tubes over a range.
It is still another feature of the present invention to provide an improved, double tube, liquid sight monitor, the annulus therebetween being capable of being purged and sealed to isolate the environment from the internal tube.